Carbon fibers and process for the production thereof

ABSTRACT

The carbon fibers of the present invention have a polymer having polar groups and groups capable of reacting with a matrix resin deposited on the fiber surfaces. The carbon fibers can be produced by depositing a monomer having both polar groups and groups capable of reacting with the matrix resin or a mixture of a monomer having polar groups and a monomer having groups capable of reacting with the matrix resin onto the fiber surface and heating to polymerize the monomer(s) forming a polymer having polar groups and groups capable of reacting with a matrix resin. The resultant fibers have excellent adhesion properties to the matrix resin and are unlikely to cause fluffing and fiber breakage.

TECHNICAL FIELD

The present invention relates to carbon fibers and a method of producingthem. In more detail, the present invention relates to carbon fibersunlikely to be fluffed by abrasion, excellent in processability,excellent in adhesion properties to a matrix resin such as anunsaturated polyester resin, vinyl ester resin, phenol resin or epoxyresin, and capable of manifesting excellent bending properties andcompressive properties as a composite material with the matrix resin,and also relates to a method of producing them.

BACKGROUND ART

Carbon fibers are being applied in such fields as sporting goods andaerospace components because of their excellent specific strength andspecific elastic modulus, and in these fields, carbon fibers are beingapplied in a wider range.

On the other hand, carbon fibers are being used also as materials forforming energy related components such as CNG tanks, fly wheels, windmills and turbine blades, as materials for reinforcing structuralcomponents of roads, bridge piers, etc. and as materials for forming orreinforcing building components such as timbers and curtain walls.

In the expansion of application fields of carbon fibers as describedabove, the matrix resins used for producing composite materialscontaining carbon fibers include a variety of resins such as epoxyresins, unsaturated polyester resins, vinyl ester resins and phenolresins. Especially unsaturated polyester resins and vinyl ester resinsare used for small ships, boats, yachts, fishing boats, household wastewater treatment tanks, various other tanks, etc. because of low materialand molding costs. Furthermore, phenol resins are often used forinterior materials of transport vehicles such as airplanes and forbuilding members such as trusses because of their incombustibility. Inthese situations, carbon fibers excellent in adhesion properties tothese matrix resins and good in processability are being demanded.

Especially if carbon fibers impregnated with a conventional epoxy resinsizing agent are used for fiber reinforced composite materialscontaining an unsaturated polyester resin or vinyl ester resin as thematrix resin, the adhesion between the carbon fibers and the unsaturatedpolyester resin or vinyl ester resin is lower, and especially the shearstrength is lower than that between the carbon fibers and an epoxyresin, not often allowing practical application. Furthermore, thesecomposite materials are lower in adhesion in a water absorbed state thanin a dry state, and their use for fishing boats, yachts and other boatsis often avoided.

Techniques for improving the adhesion between carbon fibers andunsaturated polyester resins are disclosed. For example, it is disclosedthat the adhesion between carbon fibers and unsaturated polyester resinsis improved by using an urethane compound with unsaturated groups(Japanese Patent Laid-Open Kokai) Nos. Sho56-167715 or Sho63-50573) oran ester compound with unsaturated groups at the ends (Japanese PatentLaid-Open (Kokai) No. Sho63-105178) as a sizing agent also acting as acoupling agent. However, their effects are insufficient, and they do notassure excellent adhesion properties for every kind of carbon fibers.Especially carbon fibers with excellent adhesion properties even in awater absorbed state have not been obtained.

Furthermore, carbon fiber reinforced phenol resin composite materialsare also low in the adhesion between carbon fibers and the matrix resinas in the case of unsaturated polyester resins and vinyl ester resins,and the excellent mechanical properties peculiar to carbon fibers arenot sufficiently utilized. Accordingly, as a technique for improving theadhesion between carbon fibers and phenol resins, Japanese PatentLaid-Open (Kokai) No. Hei1-172428 discloses a method of improvingadhesion by air oxidation treatment and titanate coupling agenttreatment. However, the improvement is still insufficient.

Moreover, since carbon fibers are essentially stiff, brittle and poor inbindability, bending ability and abrasion resistance, they are likely tobe fluffed or broken. Accordingly, they are usually impregnated with asizing agent, but conventional sizing agents are insufficient inimproving the bending ability and abrasion resistance of carbon fibers.It can happen that if such carbon fibers are sophisticatedly processed,for example, woven into a fabric or filament-wound, they are rubbed byguide bars, rollers, etc., to be fluffed and broken, remarkably loweringworking convenience and quality. At present, carbon fibers with highadhesion properties to resins and high sophisticated processability havenot yet been obtained.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide carbon fibers unlikelyto be fluffed and broken even when rubbed by guide bars and rollers insophisticated processing and excellent in adhesion to matrix resins, andcapable of manifesting excellent bending properties and compressiveproperties as composite materials, and also to provide a method ofproducing them.

To achieve the object of the present invention, the carbon fibers of thepresent invention are constituted as follows: Carbon fibers,characterized in that a polymer having polar groups and groups capableof reacting with a matrix resin is deposited on the fiber surfaces. In apreferable embodiment of the present invention, the polymer issubstantially insoluble in the matrix resin and covers the fibersurfaces.

The carbon fibers of the present invention can be favorably produced bya production method, comprising the steps of heating carbon fibers, onthe surfaces of which a monomer having polar groups and groups capableof reacting with the matrix resin is deposited, and polymerizing saidmonomer.

THE BEST EMBODIMENTS OF THE INVENTION

The present invention is described below in more detail.

The carbon fibers of the present invention are characterized in that apolymer having polar groups and groups capable of reacting with thematrix resin are deposited on the fiber surfaces.

A polar group is a functional group having a polarized charge and agroup capable of reacting with a matrix resin is a functional groupcapable of being chemically bonded to the matrix resin. In the carbonfibers, on the surfaces of which a polymer having these two kinds offunctional group is deposited, since the polymer is diffused into amatrix resin at a low rate, the polar groups are strongly combined withthe surfaces of carbon fibers while the groups capable of reacting withthe matrix resin are chemically bonded to the matrix resin when thecarbon fibers are used to mold a composite material, so, the obtainedcomposite material can have high adhesion properties.

The mechanism by which such effects are manifested is considered to beas follows. If functional groups being polarized exist near the surfacesof carbon fibers, the basal planes or edge planes of the graphitestructure on the carbon fiber surfaces adjacent to the polar groups arepolarized, and electric attraction occurs between the polar groups andthe carbon fiber surfaces. The adhesive strength is smaller than that ofhydrogen bonds, but since the graphite structure exists over the entirecarbon fiber surfaces, high adhesion can be obtained as a whole. Tofurther enhance the adhesion in combination with hydrogen bonds, it iseffective that a certain surface oxygen concentration, especially acertain amount of carboxyl groups exist on the carbon fiber surfaces. Inthis mechanism, it is essentially required that the compound with polargroups is localized on the carbon fiber surfaces. Therefore, it isimportant that the polymer having polar groups is formed as ahomogeneous film on the carbon fiber surfaces, and that the polymer isnot diffused into the matrix resin. Thus, the present invention is basedon a quite new concept that the hitherto unheeded dipole-dipoleinteraction with the graphite structure of carbon fiber surfaces is usedand fixed on the carbon fiber surfaces, in addition to the chemicaladhesion with the matrix resin.

In the present invention, the polymer having polar groups and groupscapable of reacting with the matrix resin is obtained by polymerizing alow molecular weight compound, specifically a monomer with a molecularweight (chemical formula weight) of 1000 or less. The polymer is notlimited in molecular weight as far as it is substantially insoluble inthe matrix resin, but to suppress diffusion, it is preferable that theweight average molecular weight is 2000 to 1,000,000, though it is onlyrequired that the polymer is substantially insoluble in the matrixresin. A low molecular weight compound having both polar groups andgroups capable of reacting with the matrix resin can be used as amonomer, or both a low molecular weight compound having polar groups anda low molecular weight compound having groups capable of reacting withthe matrix resin can also be used as monomers.

The polar groups which can be used here include those containingnitrogen such as nitro groups, nitroso groups, amino groups, methylaminogroups, dimethylamino groups, anilino groups, acetamido groups,benzamido groups, imino groups, phenylimino groups, hydroxyamino groups,nitroamino groups, hydrazide groups, diazo groups, azoxy groups,phenylazo groups, cyano groups, isocyano groups, carbamoyl groups,ureido groups, amidino groups, guanidido groups, urethane groups, ureagroups and amido groups, those containing sulfur such as mercaptogroups, sulfinyl groups, sulfo groups, sulfamoyl groups, methylthiogroups, ethylthio groups, tosyl groups, thiourea groups, thiourethanegroups and sulfonyl groups, and those containing a heterocycle such asα(β)-thienyl groups, α(β)-thenyl groups, α(β)-pyrrolyl groups andα(β,γ)-pyridyl groups. Especially in view of the stability andindustrial handling convenience of the compound in its application tothe carbon fiber surfaces, the polar groups can be more preferablyselected from amido groups, imido groups, urethane groups and ureagroups.

The groups capable of reacting with the matrix resin include thoselikely to cause radical reaction such as vinyl groups, acryloyl groups,methacryloyl groups, halogen-containing groups, azo groups and peroxidegroups if a vinyl ester resin or unsaturated polyester resin is used asthe matrix resin. In the present invention, having regard to thestability and industrial handling convenience of the compound in itsapplication to the carbon fiber surfaces, and the likelihood to reactwith the matrix resin, they can be preferably selected from vinylgroups, acrylate groups and methacrylate groups respectively havingunsaturated groups at the ends. Furthermore if a phenol resin is used asthe matrix resin, the groups capable of reacting with the matrix resincan be structures having hydroxybenzyl groups, hydroxyphenoxy groups,phenoxy groups, phenolic hydroxyl groups, etc. If an epoxy resin is usedas the matrix resin, the groups capable of reacting with the matrixresin can be epoxy groups, hydroxyl groups, carboxyl groups, aminogroups, etc.

In the present invention, among the polymer having polar groups andgroups capable of reacting with the matrix resin, a polymer componentsubstantially insoluble in the matrix resin covers the surfaces ofcarbon fibers. Accordingly, the diffusion of the polymer into the matrixresin is substantially suppressed, and when the carbon fibers are usedto mold a composite material, the polar groups are strongly combinedwith substantially all the surfaces of carbon fibers, and the groupscapable of reacting with the matrix resin are chemically combined withthe matrix resin. Therefore, the obtained composite material can havehigh adhesion properties stably. Furthermore, since interfaces betweenthe carbon fibers and the matrix resin are so strong as to inhibit theintrusion of water into the interfaces when water is absorbed, highadhesion properties can be obtained advantageously even when the fiberreinforced composite material absorbs water.

Being substantially insoluble in the matrix resin means being insolublein the solvent of the matrix resin. For example, if the matrix resin isa vinyl ester resin or unsaturated polyester resin, the polymer must besubstantially insoluble in styrene. If the matrix resin is a phenolresin, the polymer must be substantially insoluble in methanol. If thematrix resin is an epoxy resin, the polymer must be substantiallyinsoluble in chloroform.

It is preferable that the polymer insoluble in the matrix resin coversthe carbon fiber surfaces substantially uniformly, i.e., as a film,using the production method described later. It is preferable that thefilm thickness is 1 to 20 nm. A more preferable range is 2 to 10 nm.

To avoid hardening of the carbon fiber bundle by the deposited polymer,it is desirable that the deposited amount of the deposit containing thepolymer having the polar groups and the groups capable of reacting withthe matrix resin is 0.01 wt % to 5 wt % based on the weight of carbonfibers. A preferable range is 0.05 wt % to 2 wt %, and a more preferablerange is 0.05 wt % to 1 wt %. Furthermore, for letting the polymeruniformly cover the carbon fiber surfaces, it is desirable that amongthe polymer, the polymer component insoluble in the matrix resin isdeposited in an amount of 0.01 to 1.0 wt % to cover the fiber surfaces.If the deposited amount of the polymer component insoluble in the matrixresin is less than 0.01 wt %, the bindability of the carbon fiber bundleis insufficient, and depending on the matrix resin used, a sufficientadhesive strength may not be obtained between the carbon fibers and thematrix resin. If more than about 1 wt %, the carbon fiber bundle becomeshard though a sufficient adhesive strength can be obtained between thecarbon fibers and the matrix resin, and the gaps between the singlefibers constituting the carbon fiber bundle cannot be sufficientlyimpregnated with the matrix resins, so that voids are formed in themolded composite material. As a result, the mechanical properties of thecomposite material may decline.

In the present invention, the deposited amount of all the depositcontaining the polymer on the carbon fibers can be measured as describedbelow. 2 to 3 grams of carbon fibers with the deposit are heat-treatedin nitrogen atmosphere at 450° C. for 10 minutes, and the depositedamount of the deposit is obtained from the weights measured before andafter heat treatment.

In the present invention, the deposited amount of the polymer componentinsoluble in styrene can be measured as described below. A 500 ml beakeris charged with 2 to 4 g of carbon fibers with the deposit and 100 to200 ml of styrene, and they are washed by an ultrasonic washer(frequency 45 kHz, high frequency output 60 W) at a liquid temperatureof 20 to 30° C. for 10 minutes. Styrene is removed, and the residue iswashed with distilled water 2 or 3 times and dried at 100° C. for 60minutes. From the weights measured before and after treatment, thedeposited amount of the deposit soluble in styrene is obtained, andsubtracted from the deposited amount of all the deposit, to obtain thedeposited amount of the polymer component insoluble in styrene. Thisvalue can be an indicator of the deposited amount of the polymercomponent insoluble in a vinyl ester resin or unsaturated polyesterresin. In the examples described later, B2200 produced by Yamato K. K.is used as the ultrasonic washer.

The deposited amount of the polymer component insoluble in methanol canbe measured as described below. A general purpose reflux device is usedto reflux 2 to 3 g of carbon fibers with the deposit over methanol for 6hours and dried at 100° C. for 60 minutes. From the weights measuredbefore and after treatment, the deposited amount of the deposit solublein methanol is obtained and subtracted from the deposited amount of allthe deposit, to obtain the deposited amount of the polymer componentinsoluble in methanol. This value can be an indicator of the depositedamount of the polymer component insoluble in a phenol resin.

Furthermore, in the present invention, the deposited amount of thepolymer component insoluble in chloroform can be measured as describedbelow. A general purpose reflux device is used to reflux 2 to 3 g ofcarbon fibers with the deposit over chloroform for 6 hours and dried at100° C. for 60 minutes. From the weights measured before and aftertreatment, the deposited amount of the deposit soluble in chloroform isobtained and subtracted from the deposited amount of all the deposit, toobtain the deposited amount of the polymer component insoluble inchloroform. This value can be an indicator of the deposited amount ofthe polymer component insoluble in an epoxy resin.

In the present invention, it is desirable for improving the adhesionthat the surfaces of the carbon fibers with the polymer deposited have asurface oxygen concentration O/C ratio of 0.02 to 0.3 as measured by theX-ray photoelectron spectroscopy. A preferable range is 0.04 to 0.2, anda more preferable range is 0.06 to 0.15. It is also desirable that thesurface carboxyl group concentration COOH/C ratio as measured by thechemical modification X-ray photoelectron spectroscopy is 0.2 to 3%. Apreferable range is 0.5 to 3%. In this case, strong interaction occursbetween the polar groups of the polymer and the functional groups ofcarbon fiber surfaces, to allow strong adhesion not achieved hitherto.Thus high adhesion properties can be obtained in the composite material.If O/C is more than 0.3, an oxide layer much lower in strength than thecarbon fiber substrate may cover the carbon fiber surfaces to lower theadhesion properties of the obtained composite material, though thechemical adhesion between the polymer having the polar groups and thegroups capable of reacting with the matrix resin and the outermostcarbon fiber surfaces becomes strong. If less than 0.02, the reactivityand amount reacting with the polymer having the polar groups and thegroups capable of reacting with the matrix resin become insufficient,and it may not be expected to improve the adhesion properties of thecomposite material.

If COOH/C ratio is more than 3%, an oxide layer much lower in strengththan the carbon fiber substrate may cover the carbon fiber surfaces, andas a result, the adhesion properties of the obtained composite materialmay become low. If less than 0.2%, the reactivity and reacting amountwith the polymer having the polar groups and the groups capable ofreacting with the matrix resin become insufficient, and it may not beexpected to improve the adhesion properties of the composite material.

In the present invention, the surface oxygen concentration O/C ratio ofthe carbon fiber surfaces is measured by the X-ray photoelectronspectroscopy according to the following procedure. At first, a carbonfiber bundle is cut and the cut pieces are spread on a sample base madeof stainless steel, with the electron emitting angle set to 90°, withMgKα1,2 used as the X-ray source, and with the sample chamber internallykept at a vacuum degree of 1×10⁻⁸ Torr. In compensation for the peaksaccompanying the electrostatic charge during the measurement, thebinding energy B.E. of the main peak of C_(1S) is set at 284.6 eV. TheC_(1S) peak area is obtained by drawing a linear base line in a range of282 to 296 eV, and the O_(1S) peak area is obtained by drawing a linearbase line in a range of 528 to 540 eV. The surface oxygen concentrationO/C ratio is expressed by the atomic ratio calculated by dividing theratio of said O_(1S) peak area to C_(1S) peak area by relativesensitivity factor unique to the apparatus. In the examples describedlater, ESCA-750 produced by Shimadzu Corp. is used as the X-rayphotoelectron spectroscope, and the relative sensitivity factor of theapparatus is 2.85.

In the present invention, the surface carboxyl group concentrationCOOH/C ratio of the carbon fiber surfaces is measured by chemicalmodification X-ray photoelectron spectroscopy according to the followingprocedure. At first, a carbon fiber bundle is cut and the cut pieces arespread on a sample base made of platinum and exposed to air containing0.02 mole/liter of trifluoroethanol gas, 0.001 mole/liter ofdichlorohexylcarbodiimide gas and 0.04 mole/liter of pyridine gas at 60°C. for 8 hours, to be chemically modified. They are mounted on an X-rayphotoelectron spectroscopy with the electron emitting angle of 35°, andwith AlKα1,2 used as the X-ray source, and with the sample chamberinternally kept at a vacuum degree of 1×10⁻⁸ Torr. In compensation forthe peaks accompanying the electrostatic charge during the measurement,the binding energy B.E. of the main peak of C_(1S) is set at 284.6 eV.The C_(1S) peak area [C_(1S)] is calculated by drawing a linear baseline in a range of 282 to 296 eV, and the F_(1S) peak area [F_(1S)] iscalculated by drawing a linear base line in a range of 682 to 695 eV.Furthermore, from the C_(1S) peak split of chemically modifiedpolyacrylic acid, the reactivity rate r is calculated from the C_(1S)peak separation of polyacrylic acid, the persistence rate m wascalculated from the O_(1S) peak separation of dicyclohexylcarbodiimidederivative, which were chemically modified at the same time.

The surface carboxyl group concentration COOH/C ratio is calculated fromthe following formula:${{COOH}/C} = {\frac{\left\lbrack F_{1S} \right\rbrack}{\left( {3{k\left\lbrack {\left\lbrack C_{1S} \right\rbrack - {\left( {2 + 13} \right)\left\lbrack F_{1S} \right\rbrack}} \right)}r} \right.} \times 100(\%)}$

where k is the relative sensitivity factor of the F_(1S) peak area tothe C_(1S) peak area peculiar to the apparatus, and the relativesensitivity factor of Model SSX-100-206 produced by SSI, USA used as theX-ray photoelectron spectroscope in the examples described later is3.919.

To measure the surface oxygen concentration O/C ratio and the surfacecarboxyl group concentration COOH/C ratio in the carbon fibers with thedeposit, the carbon fibers obtained by removing the deposit according tothe following procedure are used. That is, the carbon fibers with thedeposit are refluxed over a mixture of chloroform and methanol (ratio byvolume 1:2) for 6 hours, and washed with methanol, being immersed in 98%concentrated sulfuric acid for a whole day and night, to remove thedeposit from the carbon fibers. Furthermore, the carbon fibers arewashed again with methanol and dried by a hot air dryer.

To produce the carbon fibers with the polymer deposited, as describedlater, it is preferable to deposit a sizing agent with any of saidmonomers dissolved or dispersed in a solvent, on carbon fiber surfaces,and to heat them for removing the solvent while polymerizing themonomer. The solvent which can be used in this case can be an organicsolvent such as methanol, ethanol, acetone, methyl ethyl ketone,dimethylformamide or dimethylacetamide, etc., but having regard todisaster prevention, water is preferable. Since the monomer is ofteninsoluble in water, an emulsifying agent is generally added to make anemulsion. However, since the emulsifying agent does not have either thepolar groups or the groups capable of reacting with the matrix resin, itis desirable that the ratio by weight of the monomer to the emulsifyingagent is 70˜95:30˜5. A preferable range is 80˜95:20˜5. The monomerdestined to be a polymer at this mixing ratio can easily provide astable water dispersion, and carbon fibers capable of manifesting highmechanical properties in a composite material can be obtained. If theamount of the emulsifying agent based on the weight of all the monomersis more than 30 wt %, the emulsifying agent covers the carbon fibersurfaces at a higher ratio, to lower the adhesive properties of thecomposite material, and the adhesion properties after water absorptionmay decline. If less than 5 wt %, the emulsification stability of asizing agent with water as the solvent may decline.

As the emulsifying agent, it is desirable to use a nonionic emulsifyingagent. The nonionic emulsifying agent can be one or more in combinationselected from ether type emulsifying agents such as polyoxyethylenealkyl ethers, single chain length polyoxyethylene alkyl ethers,polyoxyethylene secondary alcohol ethers, polyoxyethylene alkyl phenylethers, polyoxyethylene sterol ethers, polyoxyethylene lanolinderivatives, ethylene oxide derivatives of alkyl phenol formalincondensation products, polyoxyethylene polyoxypropylene block copolymerand polyoxyethylene polyoxypropylene alkyl ethers, ether ester typeemulsifying agents such as polyoxyethylene glycerol fatty acid esters,polyoxyethylene castor oil and hardened castor oil, polyoxyethylenesorbitan fatty acid esters and polyoxyethylene sorbitol fatty acidesters, and ester type emulsifying agents such as polyethylene glycolfatty acid esters and polyglycerol fatty acid esters. Preferably usednonionic emulsifying agents include alkylene oxide (e.g., ethyleneoxide, propylene oxide or butylene oxide) addition products (block orrandom addition products in the case of two or more alkylene oxideaddition products) of phenols selected from (1) monocyclic phenols(phenols having one aromatic ring) such as phenol, phenols having one ormore alkyl groups, and polyhydric phenols and (2) polycyclic phenols(phenols with two or more aromatic rings) such as phenylphenol,cumylphenol, benzylphenol, hydroquinone monopheyl ether, naphthol,bisphenol, reaction products (styrenated phenols) between a monocyclicphenol or polycyclic phenol, etc. and a styrene (styrene orα-methylstyrene, etc.), etc. Among them, an ethylene oxide additionproduct or propylene oxide addition product of a styrenated phenol canbe preferably used. The method for adding an alkylene oxide to such aphenol can be any ordinary method. It is preferable that the number ofmoles added is 1 to 120. A more preferable range is 10 to 90, and anespecially preferable range is 30 to 80.

In addition to the nonionic emulsifying agent, an anionic surfactantsuch as a carboxylate, sulfonate, sulfate or phosphate, a cationicsurfactant such as an aliphatic amine salt or fatty acid quaternaryammonium salt or an amphoteric surfactant such as carboxybetaine type oraminocarboxylate can also be used for further stabilizing the emulsion.

When an unsaturated polyester or vinyl ester resin is used as the matrixresin, a compound obtained by letting an unsaturated alcohol or anunsaturated carboxylic acid and an isocyanate compound react with eachother can be suitably used as the monomer. A compound obtained byletting an unsaturated alcohol and an isocyanate compound react witheach other can be especially suitably used.

The unsaturated alcohols which can be used here include olefin alcohols,reaction products between an unsaturated carboxylic acid and a polyol,etc. The olefin alcohols include, for example, allyl alcohol, crotylalcohol, 3-butene-1-ol, 3-butene-2-ol, 3-pentene-1-ol, 4-pentene-1-ol,4-pentene-2-ol, 4-hexene-1-ol, 5-hexene-1-ol, etc., and an olefinalcohol with unsaturated groups at the ends is preferably suitable forenhancing the molecular weight described later. The reaction productsbetween an unsaturated carboxylic acid and a polyol include, forexample, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,2-(meth)acryloyloxyethylphthalic acid,2-hydroxy-3-(meth)acryloyloxypropyl (meth)acrylate, ethylene glycolmono(meth)acrylate, diethylene glycol mono(meth)acrylate, polyethyleneglycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate,polyethylene glycol polypropylene glycol mono(meth)acrylate,1,6-hexanediol mono(meth)acrylate, neopentyl glycol mono(meth)acrylate,trimethylolpropane di(meth)acrylate, bisphenol A diglycidyl ether(meth)acrylic acid addition product, etc. A reaction product between anunsaturated carboxylic acid and a polyol can be preferably used.

The unsaturated carboxylic acids which can be used here include acrylicacid, methacrylic acid, oleic acid, maleic acid, fumaric acid, itaconicacid, etc. The polyols which can be preferably used here include, forexample, glycerol, ethylene glycol, diethylene glycol, polyethyleneglycol, polypropylene glycol, polyalkylene glycol, arabitol, sorbitol,1,6-hexanemethylene diol, etc.

The isocyanate compounds which can be used here include, for example,known isocyanate compounds such as tolylene diisocyanate, ditolylenediisocyanate, diphenylmethane diisocyanate, dimethyldiphenylmethanediisocyanate, hexamethylene diisocyanate, metaphenylene diisocyanate,propyl isocyanate, and butyl isocyanate. Especially to ensure theflexibility of the carbon fiber bundle after application to the carbonfibers, an aliphatic structure without containing any aromatic ring suchas 1,6-hexamethylene diisocyanate, propyl isocyanate or butyl isocyanatecan be preferably used.

Any of the above unsaturated alcohols or any of the above unsaturatedcarboxylic acids and any of the above isocyanate compounds are properlycombined, and proper reaction conditions are selected from knownurethanation reaction conditions. After completion of reaction, thereaction solvent is removed, to easily obtain the intended compound.

As the reaction product, an unsaturated polyurethane compound withacrylate groups and methacrylate groups as the unsaturated groups at theends is preferable, and at least one compound selected fromphenylglycidyl ether acrylate hexamethylene diisocyanate, phenylglycidylether acrylate tolylene diisocyanate, pentaerythritol acrylatehexamethylene diisocyanate, phenylglycidyl ether triacrylate isophoronediisocyanate, glycerol dimethacrylate tolylene diisocyanate, glyceroldimethacrylate isophorone diisocyanate, pentaerythritol triacrylatetolylene diisocyanate, pentaerythritol triacrylate isophoronediisocyanate and triallyl isocyanurate can be used.

It is preferable that the number of unsaturated groups at the ends istwo or more per monomer molecule, for easily and uniformly enhancing themolecular weight on the carbon fiber surfaces to form a film and forcausing reaction with an unsaturated polyester resin or vinyl esterresin. Three or more unsaturated groups are more preferable. If amonomer with one unsaturated group at an end is heated and polymerizedon the carbon fiber surfaces, the reaction with the matrix resin doesnot progress since the number of functional groups capable of reactingwith the matrix resin is small, and it can happen that the adhesionproperties of the composite material do not improve.

To ensure the interaction with a specific amount of functional groups onthe carbon fiber surfaces when a film is formed on the carbon fibersurfaces, it is preferable that the polar group density as the number ofpolar groups per molecular weight (chemical formula weight) of themonomer is 1×10⁻³ or more per molecular weight. A polar group density of3×10⁻³ or more per molecular weight is more preferable. Usually theupper limit is 15×10⁻³ or less per molecular weight, and preferable is7×10⁻³ or less per molecular weight.

As for the structure of a preferable low molecular weight compound, aflexible aliphatic compound which allows the molecular weight to beraised easily on the carbon fiber surfaces, does not have anythree-dimensionally large stiff compound at the interfaces between thecarbon fibers and the matrix resin and has molecular chains without anyaromatic ring arranged linearly is preferable. Especially an aliphaticpolyisocyanate compound having unsaturated groups at the ends and polargroups, i.e., a polyisocyanate compound having a polyethylene glycolstructure and a polyalkylene structure is preferable since the polymercan be deposited on the carbon fiber surfaces to improve both abrasionresistance and fluff resistance.

It is preferable that the molecular weight (chemical formula weight) ofthe compound is 300 to 2000 for preventing that its handling convenienceas a bundling agent becomes poor due to a high resin viscosity. A morepreferable range is 500 to 1000.

If a phenol resin is used as the matrix resin, highly reactivehydroxybenzyl groups, hydroxyphenoxy groups, phenoxy groups and phenolichydroxyl groups are especially preferable as the groups capable ofreacting with the matrix resin having regard to the stability andindustrial handling convenience of the compound in its application tocarbon fibers. Low molecular weight compounds having both the groupscapable of reacting with a phenol resin and the polar groups, which canbe used here include phenylglycidyl ether acrylate. hexamethylenediisocyanate, phenylglycidyl ether tolylene diisocyanate andphenylglycidyl ether isophorone diisocyanate.

When a low molecular weight compound having the polar groups and a lowmolecular weight having the groups capable of reacting with a phenolresin are used as monomers to make a copolymer, it is desirable to usean aromatic compound having unsaturated groups at the ends andhydroxybenzyl groups, hydroxyphenoxy groups, phenoxy groups or phenolichydroxyl groups as the former low molecular weight compound and to use acompound having the polar groups and unsaturated groups at the ends asthe latter low molecular weight compound. Specifically the compoundswhich can be used as the former low molecular weight compound include2-allylphenol, phenoxyethyl (meth)acrylate, phenoxy polyethylene glycol(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, etc.

If an epoxy resin is used as the matrix resin, the groups capable ofreacting with the matrix resin should be highly reactive epoxy groups,and having regard to the stability and industrial handling convenienceof the compound in its application to carbon fibers, an epoxy compoundhaving a hydantoin structure or an epoxy compound having an isocyanuratestructure, etc. can be used as the monomer having both the groupscapable of reacting with the matrix resin and the polar groups.

When a lower molecular weight compound having the polar groups and alower molecular weight compound having the groups capable of reactingwith an epoxy resin are used as monomers to make a copolymer, it isdesirable to use a compound having unsaturated groups at the ends andepoxy groups as the former low molecular weight compound and to use acompound having the polar groups and unsaturated groups at the ends asthe latter low molecular weight compound. Specifically the compoundswhich can be used as the former low molecular weight compound includeglycidol, glycidyl methacrylate, glycidyl methacrylate ethylene oxideaddition product, glycidyl methacrylate ethylene oxide/propylene oxideblock copolymer addition product, etc.

It is preferable that the carbon fibers of the present invention have astrand strength of 3000 MPa or more. More preferable is 4000 MPa ormore, and still more preferable is 4500 MPa or more. Furthermore, it ispreferable that the strand modulus is 200 GPa or more. More preferableis 220 GPa or more. The composite material obtained by using such carbonfibers can manifest desired properties. The strand strength and strandmodulus of carbon fibers refer to the strength and modulus measuredaccording to the resin impregnated strand testing methods of JIS R 7601using a resin consisting of Bakelite (registered trademark) ERL4221/3produced by Union Carbide/boron fluoride monoethylamine/acetone=100/3/4(parts by weight). It is preferable that the strand strength and modulusare larger, but at present their upper limits are about 7000 MPa and 800GPa respectively.

The method for producing the carbon fibers of the present invention aredescribed below.

The carbon fibers of the present invention can be obtained by depositinga monomer having polar groups and groups capable of reacting with amatrix resin on the fiber surfaces, heating the carbon fibers andpolymerizing the monomer. Specifically the monomer is deposited on acarbon fiber bundle which is preliminarily dried by a heating roller andprimarily dried using a hot air dryer, and then the monomer is thermallypolymerized. After the monomer is deposited, the fiber bundle can beopened to be fixed in the opened state by preliminarily drying using aheating roller, as so-called thermal fixing. Furthermore, it ispreferable to carry out the primary drying and the thermalpolymerization simultaneously since the obtained carbon fiber bundle canbe kept flexible. If flexibility can be ensured, the preliminary dryingcan also be omitted.

To make the monomer deposited on the fiber surfaces, at first, a sizingsolution with the monomer dissolved or dispersed in a solvent such aswater, methanol, ethanol, dimethylformamide, dimethylacetamide oracetone, etc. is prepared, and the fibers are immersed in the sizingsolution by feeding over a roller, or the fibers can be brought intocontact with a roller with the sizing solution deposited on it, or thesizing solution can be blown onto the fibers as a mist. This process canbe effected by batch operation, but for higher productivity and smallervariation, continuous operation is desirable. In this case, to provide asuitable amount of the monomer deposited uniformly onto the carbonfibers, it is preferable to control the monomer content in the sizingsolution, the temperature of the sizing solution, the tension applied tothe fibers, etc., and as required, to ultrasonically vibrate the carbonfibers. Furthermore, as the solvent used for the sizing solution, wateris preferable since it is easy to handle having regard to disasterprevention.

For uniform application of the monomer into the carbon fiber bundle, itis important to preliminarily dry the carbon fibers by a heating rollerwhile opening it, for thermal fixing. The opening and thermal fixingallows the monomer to be uniformly applied into the carbon fiber bundleand can prevent the excessive bindability of the carbon fiber bundle inthe subsequent step of thermal polymerization, for keeping the carbonfiber bundle flexible. The effect can be more remarkably observed when acarbon fiber bundle consisting of more than 10,000 filaments, especiallymore than 15,000 filaments is used. It is preferable that the thermallydrying roller temperature in this case is insufficient for drying toprevent the fluffing and filament breaking caused otherwise when thedrying in the opened state is perfect, i.e., a range from 100° C. to200° C. which is lower than the primary drying temperature stated below.

The carbon fibers with the sizing solution deposited thereon have thesolvent substantially perfectly removed by the primary drying, and areheat-treated to polymerize the monomer on the fiber surfaces. It ispreferable to effect the step of heat treatment for primary drying andthe step of heat treatment for polymerizing the monomer simultaneously,since the productivity is higher and since the monomer can bepolymerized with the fiber bundle opened to keep the carbon fiber bundleflexible.

Furthermore, in the present invention, to keep the insoluble matter inthe matrix resin at a specific amount, it is preferable to enhance themolecular weight on the carbon fiber surfaces, and for this purpose, itis preferable that the drying temperature is higher than thepolymerization initiation temperature. It is preferable that the dryingtemperature is 150° C. to 350° C. A more preferable range is 180° C. to300° C., and an especially more preferable range is 200° C. to 250° C.The treatment time depends on the heat treatment temperature, but it ispreferable that the treatment time is 30 seconds to 30 minutes. A morepreferable range is 50 seconds to 15 minutes.

Such auxiliary ingredients as an emulsifying agent and a surfactant forimproving the handling convenience, abrasion resistance and fluffresistance of carbon fibers can also be added to the sizing solution.Furthermore, to still improve the bindability, etc., another compoundsuch as a polyurethane, polyester or epoxy resin can also be added tothe sizing solution, but to keep the polar group density in the deposit,it is preferable that the added amount of these compounds is kept at 30wt % or less of all the deposit. More preferable is 15 wt % or less.

Raw carbon fibers which can be used here include acrylic carbon fibers,pitch based carbon fibers, rayon based carbon fibers, etc. Among them,acrylic carbon fibers are preferable since long fibers with a highstrength are likely to be obtained. The method for producing acryliccarbon fibers as raw carbon fibers is described below.

As for the spinning method for obtaining acrylic fibers, wet spinning,dry spinning, semi-wet spinning, etc. can be used. However, wet spinningor semi-wet spinning is preferable since high strength fibers are likelyto be obtained, and semi-wet spinning is more preferable. The spinningdope used is a solution or suspension of polyacrylonitrile homopolymeror copolymer. The fibers formed by any of the above spinning methods areusually washed with water, drawn and oiled to make precursor fibersdestined to be carbon fibers. The precursor fibers are stabilized in anoxidizing atmosphere such as air at 200 to 300° C. and carbonized in aninactive atmosphere such as nitrogen with the maximum temperature keptat higher than 1200° C., preferably higher than 1300° C. Furthermore, asrequired, they may be graphitized. To improve the strength and modulusof carbon fibers, it is preferable to keep the diameter of singlefilaments small, specifically at 10 μm or less. More preferable is 8 μmor less, and still more preferable is 6 μm or less.

The carbonized or graphitized fibers are further oxidized on thesurfaces. As the surface oxidation treatment, electrolytic surfacetreatment for electrochemically oxidizing with fibers as the anode ispreferable. The electrolytic solution used for the electrolytic surfacetreatment can be either an acid aqueous solution or alkaline aqueoussolution. However, an acid aqueous solution is desirable since thecarboxyl group concentration COOH/C ratio of fiber surfaces can beeasily increased.

The acid electrolyte can be any compound which becomes acid as anaqueous solution. The acid electrolytes which can be used here includeinorganic acids such as sulfuric acid, nitric acid, hydrochloric acid,phosphoric acid, boric acid and carbonic acid, organic acids such asacetic acid, butyric acid, oxalic acid, acrylic acid and maleic acid,and salts such as ammonium sulfate and ammonium hydrogensulfate. Amongthem, sulfuric acid and nitric acid which show strong acidity arepreferable. The alkaline electrolyte can be any compound which becomesalkaline as an aqueous solution. The alkaline electrolytes which can beused here include hydroxides such as sodium hydroxide, potassiumhydroxide and barium hydroxide, ammonia, inorganic salts such as sodiumcarbonate and sodium hydrogencarbonate, organic salts such as sodiumacetate and sodium benzoate, their potassium salts, barium salts andother metal salts, ammonium salts and organic compounds such ashydrazine. It is preferable to use inorganic alkalis such as ammoniumcarbonate and ammonium hydrogencarbonate which do not contain any alkalimetal causing the problem of hardening with the resin. It is morepreferable to use tetraalkylammonium hydroxides which show strongalkalinity.

It is preferable that the electrolyte concentration in the electrolyticsolution is 0.01 to 5 moles/liter. A more preferable range is 0.1 to 1mole/liter. It is preferable that the temperature of the electrolyticsolution is 0 to 100° C. More preferable is room temperature.

The quantity of electrolytic treatment is optimized to suit thecarbonization temperature of the carbon fibers to be electrolyticallytreated on the surfaces. High modulus fibers carbonized at highertemperatures require a larger quantity of electrolytic treatment, but itis preferable that the quantity of electrolytic treatment is 1 to 1000coulombs/g (coulombs per 1 g of carbon fibers) for promoting the declineof crystallinity in the surface layer, improving productivity,preventing the decline of strength of the carbon fiber substrate andkeeping the decline of crystallinity in the surface layer in a moderaterange. A more preferable range is 3 to 300 coulombs/g. The time takenfor the electrolytic surface treatment should be optimized withreference to the quantity of electrolytic treatment and theconcentration of the electrolyte solution, but having regard toproductivity a preferable range is several seconds to about 10 minutes.A more preferable range is 10 seconds to about 2 minutes. Having regardto safety, it is preferable that the electrolytic voltage in theelectrolytic surface treatment is 25 V or less. A more preferable rangeis 0.5 to 20 V. The electrolytic surface treatment can be carried out bybatch operation, but for higher productivity and less variation,continuous operation is desirable. As for the method of electrolyzingthe fibers, either the direct electrolyzation to bring the carbon fibersinto direct contact with an electrode roller or the indirectelectrolyzation to energize with an electrolytic solution, etc. keptbetween the carbon fibers and the electrode can be used. However, it isdesirable to adopt the indirect electrolyzation since the fluffing,electric sparks, etc. during electrolytic treatment can be prevented. Asfor the electrolyzer used for the electrolytic surface treatment,electrolytic cells, as many as necessary, can be connected in series forcontinuous treatment, or one electrolytic cell can be used for treatmentrepetitively as often as necessary. It is preferable that the length ofthe cathode cell with a cathode immersed therein is 10 to 1000 mm. Amore preferable range is 300 to 900 mm. When the indirectelectrolyization is adopted, it is preferable that the length of theanode cell with an anode immersed therein is 5 to 100 mm.

The electrolytic surface treated fibers are then washed with water anddried. If the drying temperature in this case is too high, thefunctional groups, especially carboxyl groups existing on the outermostsurfaces of carbon fibers are likely to vanish because of thermaldecomposition. Accordingly, it is preferable to dry at a temperature aslow as possible, specifically at 100° C. to 250° C. A more preferablerange is 100° C. to 210° C., and a still more preferable range is 100°C. to 180° C.

Undergoing such a step of surface oxidation treatment is suitable forobtaining raw carbon fibers having fiber surfaces showing the saidspecific surface oxygen concentration O/C ratio and surface carboxylgroup concentration COOH/C ratio.

EXAMPLES

The present invention is described below more specifically withreference to examples. In these examples, unidirectional test pieces offiber reinforced composite materials were prepared as described below.

A vinyl ester resin composite material was obtained by setting ametallic frame with carbon fibers wound around it in unidirection into amold, pouring 100 parts of a vinyl ester resin (Ripoxy (registeredtrademark) R806 produced by Showa Highpolymer), 0.5 part of cobaltnaphthenate (Cobalt N produced by Showa Highpolymer) and 1.0 part ofmethyl ethyl ketone peroxide (Permeck N produced by NOF Corp.) into themold, deaerating in vacuum, press-molding (at room temperature for 24hours), and post-hardening at 120° C. for 2 hours, to obtain a moldedvinyl ester resin board with a fiber content of 55 to 65 vol %.

An unsaturated polyester resin composite material was obtained bysetting a metallic frame with carbon fibers wound around it inunidirection into a mold, pouring 100 parts of an unsaturated polyesterresin (Polymal 8225P(W) produced by TakedaChemical) and 0.5 part ofmethyl ethyl ketone peroxide (Permeck N produced by NOF Corp.) into themold, deaerating in vacuum, press-molding (at room temperature for 24hours), and post-hardening at 120° C. for 2 hours, to obtain a moldedunsaturated polyester resin board with a fiber content of 55 to 65 vol%.

A phenol resin composite material was obtained by setting a metallicframe with carbon fibers wound around it in unidirection into a mold,pouring 100 parts of a phenol resin (BRL-240 produced by ShowaHighpolymer) and 30 parts of a hardening catalyst (FRH-30 produced byShowa Highpolymer ) into the mold, deaerating in vacuum, andpress-molding (at 60° C. for 2 hours and at 150° C. for 1 hour), toobtain a molded phenol board with a fiber content of 55 to 65 vol %.

An epoxy resin composite material was obtained by setting a metallicframe with carbon fibers wound around it in unidirection into a mold,pouring 100 parts of an epoxy resin (Epikote (registered trademark) 828produced by Yuka Shell) and 3 parts of a hardening catalyst (BF3.MEA)into the mold, deaerating in vacuum, and press-molding (at 170° C. for 1hour), to obtain a molded epoxy resin board with a fiber content of 55to 65 vol %.

The mechanical properties of fiber reinforced composite materials wereobtained as described below.

The inter-layer shear strength hereinafter abbreviated as ILSS) wasobtained by testing a unidirectional 2.5 mm thick, 6 mm wide and 16 mmlong test piece using an ordinary three-point bending test jig (indenter10 mm dia. fulcrum 4 mm dia.) at a support span of 14 mm at a strainrate of 2.6 mm/min.

The ILSS after water absorption was obtained by immersing a similar testpiece to the above into distilled water at 98 to 100° C. for 16 hours,and measuring as described above in the water absorbed state.

The bending strength was obtained by testing a unidirectional 2 mmthick, 15 mm wide and 100 mm long test piece using a three-point bendingtest jig (indenter 10 mm dia., fulcrum 10 mm dia.) at a support span of80 mm at a strain rate of 1.5 mm/min.

The compressive strength was obtained according to Method A of JIS K7076 using a molded unidirectional 1 mm thick board.

Furthermore the sophisticated processability of carbon fibers in theexamples was evaluated according to the following methods.

For the abrasion fluff, an abrasion device was used, in which fivestainless rods with a diameter of 10 mm (chromium plated, surfaceroughness 1˜1.5 S) were arranged in parallel to each other at 50 mmintervals in such a zigzag manner that a carbon fiber yarn could passover their surfaces in contact with them at a contact angle of 120°. Thecarbon fiber yarn was passed through the device at an inlet tension of0.09 g per denier at 3 m/min, and a laser beam was applied from alateral side in a direction perpendicular to the yarn. The number offluff particles was counted by a fluff detector and expressed inpieces/m.

The flexibility of a carbon fiber bundle (hereinafter expressed as theflexibility of a CF bundle) was evaluated by touching the carbon fiberbundle. If the carbon fiber bundle was bent when it was touched withoutapplying any force and if it could be easily separated into singlefilament sets respectively consisting of less than about tens offilaments, the flexibility was judged to be good. On the other hand, ifthe carbon fiber bundle was bent with a force applied without beinglittle divided into sets of filaments, the flexibility was judged to bepoor.

Example 1

A copolymer consisting of 99.4 mol % of acrylonitrile (AN) and 0.6 mol %of methacrylic acid was spun by semi-wet spinning to obtain an acrylicfiber bundle consisting of 12000 filaments with a single filamentfineness of 1.1 deniers. The obtained fiber bundle was heated in 240 to280° C. air at a drawing ratio of 1.0, to be converted into stabilizedfibers, and they were drawn by 5% in a nitrogen atmosphere at a heatingrate of 200° C./min in a temperature range from 300 to 900° C., andcarbonized up to 1300° C. while being contracted by 3%. The yield of theobtained carbon fibers was 0.80 g/m, and the specific weight was 1.80.

The carbon fibers were electrolytically treated on the surfaces using0.1 mole/liter sulfuric acid in aqueous solution as the electrolyte at 5coulombs per 1 g of carbon fibers. The electrolytically surface treatedcarbon fibers were in succession washed with water and dried in 150° C.heating air, to obtain raw carbon fibers. The surface oxygenconcentration O/C ratio and surface carboxyl group concentration COOH/Cratio of the raw carbon fibers are shown in Table 1.

In succession, glycerol dimethacrylate hexamethylene diisocyanate(monomer A: molecular weight 625) (UA101H produced by Kyoeisha Chemical)as a monomer having urethane groups as the polar groups and methacryloylgroups as the groups capable of reacting with a vinyl ester resin Wasdiluted by acetone, to prepare a sizing solution, and applied to the rawcarbon fibers by immersion. The raw carbon fibers impregnated with thesizing solution was preliminarily dried by a hot roller at 150° C. for 5seconds, and primarily dried and polymerized at 230° C. for 120 seconds.The deposited amount of all the deposit was 1.1 wt %, and the depositedamount of the polymer component insoluble in styrene was 0.15 wt %.

The carbon fibers obtained in this manner had a strand strength of 5.2GPa and a strand modulus of 240 GPa. The ILSS of the composite materialwith the vinyl ester resin as the matrix resin was 85 MPa, and the ILSSof the composite material after water absorption was 77 MPa, showing aretension ratio of 91%. Thus, the composite material had high adhesionproperties and high water absorption resistance. The bending strengthwas 1350 MPa and the compressive strength was 1170 MPa. The abrasionfluff was as few as 3 pieces/m, and the flexibility of the CF bundle wasgood, showing that the carbon fiber bundle had high sophisticatedprocessability.

Examples 2 and 3

Carbon fibers of on which the deposited amount of all the deposit was1.0 wt % (Example 2) and carbon fibers on which the deposited amount ofall the deposit was 1.2 wt % (Example 3) were obtained as described forExample 1, except that the pentaerythritol triacrylate hexamethylenediisocyanate (monomer B: molecular weight 765) (UA306H produced byKyoeisha Chemical) as a monomer having urethane groups as the polargroups and acryloyl groups and methacryloyl groups as the groups capableof reacting with the matrix resin or phenyl glycidyl ether acrylatehexamethylene diisocyanate (monomer C: molecular weight 613) (AH600produced by Kyoeisha Chemical) was used as the monomer. Respectiveproperties of the composite materials with the vinyl ester resin as thematrix resin were measured, and the results, etc. are shown in Table 1.

Example 4

Carbon fibers on which the deposited amount of all the deposit was 1.2wt% were obtained as described for Example 1, except that phenyl glycidylether acrylate tolylene diisocyanate (monomer D: molecular weight 619)(AT600 produced by Kyoeisha Chemical) with an aromatic structure wasused as the monomer. Respective properties of the composite materialwith the vinyl ester resin as the matrix resin were measured, and theresults, etc. are shown in Table 1.

Comparative Example 1

Carbon fibers on whichthe deposited amount of all the deposit was 1.0 wt% were obtained as described for Example 1, except thattrimethylolpropane triacrylate without having any polar groups was usedas the monomer. Respective properties of the composite material with thevinyl ester resin as the matrix resin were measured, and the results,etc. are shown in Table 1. The ILSS was 75 MPa, and the ILSS after waterabsorption was 58 MPa, showing a low retention ratio of 77%. The bendingstrength was 1250 MPa, and the compressive strength was 1080 MPa,respectively being much lower than those of Example 1. The abrasionfluff was 5 pieces/m, and the flexibility of the CF bundle was good.

Comparative Example 2

Carbon fibers were obtained as described for Example 1, except that nomonomer was added. Respective properties of the composite material withthe vinyl ester resin as the matrix resin were measured, and theresults, etc. are shown in Table 1. The ILSS was 76 MPa, and the ILSSafter water absorption was 60 MPa, showing a low retention ratio of 79%.The bending strength was 1260 MPa and the compressive strength was 1060MPa, respectively being much lower than those of Example 1. The abrasionfluff was as many as 20 pieces/m, and the flexibility of the CF bundlewas good.

Comparative Example 3

Carbon fibers were obtained as described for Example 1, except that anepoxy resin (Epikote (registered trademark) 828, produced by Yuka Shell)was used as the monomer. Respective properties of the composite materialwith the vinyl ester resin as the matrix resin were measured, and theresults are shown in Table 1. The ILSS was 77 MPa, and the ILSS afterwater absorption was 57 MPa, showing a low retention ratio of 74%. Thebending strength was 1250 MPa and the compressive strength was 1070 MPa,respectively being much lower than those of Example 1. The abrasionfluff was 6 piece/m, and the flexibility of the CF bundle was ratherpoor.

Examples 5 and 6

Carbon fibers were obtained as described for Example 1, except that thequantity of electrolytic treatment was changed to 10 or 40 coulombs/g.The deposited amounts of all the deposits were 1.2 wt % and 1.3 wt %respectively. Respective properties of the composite materials with thevinyl ester resin as the matrix resin were measured, and the results,etc. are shown in Table 1.

Example 7

Carbon fibers on which the deposited amount of all the deposit was 1.1wt % were obtained as described for Example 1, except that the dryingtemperature after the electrolytic surface treatment was 250° C.Respective properties of the composite material with the vinyl esterresin as the matrix resin were measured, and the results, etc. are shownin Table 1.

Examples 8 to 10

Carbon fibers were obtained as described for Example 1, except that thethermal polymerization temperature after applying the monomer waschanged to 180° C., 150° C. or 80° C. The deposited amounts of all thedeposits were 1.2 wt %, 1.2 wt % and 1.1 wt % respectively. Respectiveproperties of the composite materials with the vinyl ester resin as thematrix resin were measured, and the results, etc. are shown in Table 2.

Examples 11 to 13

Carbon fibers were obtained as described for Example 1, except thatbisphenol S diglycidyl dimethacrylate as a monomer having sulfo groupsas the polar groups and methacryloyl groups as the groups capable ofreacting with the vinyl ester resin, N,N-dimethylaminoethyl acrylate asa monomer having amino groups as the polar groups and acryloyl groups asthe groups capable of reacting with the vinyl ester resin, or end acrylmodified liquid butadiene (TE2000 produced by Nippon Soda) as a monomerhaving urethane groups as the polar groups and end vinyl groups as thegroups capable of reacting with the vinyl ester resin was used as themonomer. The deposited amounts of all the deposits were 1.2 wt %, 0.9 wt% and 1.3 wt % respectively. Respective properties of the compositematerials with the vinyl ester resin as the matrix resin were measured,and the results, etc. are shown in Table 3.

Example 14

Glycerol dimethacrylate hexamethylene diisocyanate (monomer A) as amonomer having urethane resins as the polar groups and methacryloylgroups as the groups capable of reacting with the vinyl ester resin wasdispersed into water using polyoxyethylene (70-mole) styrenated (5-mole)cumylphenol (ratio by weight 90:10) (emulsifying agent A) as a nonionicemulsifying agent to prepare a sizing solution, and it was applied tothe raw carbon fibers used in Example 1 by immersion. The carbon fibersimpregnated with the sizing solution were dried by a 150° C. hot dryingroller for 5 seconds, and in succession heat-treated by a hot aircirculation type dryer at 230° C. for 60 seconds. The deposited amountof all the deposit was 0.6 wt %, and the amount of the matter insolublein styrene was 0.15 wt %.

The abrasion fluff of the obtained carbon fibers, the flexibility of theCF bundle, the ILSS of the composite material with the vinyl ester resinas the matrix resin, and the bending strength were measured, and theresults are shown in Table 4. The compressive strength was 1160 MPa.

Examples 15 to 17

Carbon fibers were obtained as described for Example 14, except that theratio of the monomer to the emulsifying agent was changed. Respectiveproperties were measured and the results are shown in Table 4.

Examples 18 and 19

Carbon fibers were obtained as described for Example 14, except that thedrying temperature after the electrolytic surface treatment was changedto 150° C. or 180° C. and that the deposited amount of the polymercomponent insoluble in styrene was changed to 0.05 wt % or 0.10 wt %.Respective properties were measured, and the results are shown in Table4.

Examples 20 and 21

Carbon fibers were obtained as described for Example 14, except that thedeposited amount of all the deposit was changed to 1.0 wt % or 0.10 wt%. Respective properties were measured and the results are shown inTable 4.

Comparative Example 4

Carbon fibers were obtained as described for Example 14, except that anepoxy resin (Epikote (registered trademark) 828, produced by Yuka Shell)was used as the monomer. Respective properties were measure and theresults are shown in Table 4. The compressive strength of the compositematerial with the vinyl ester resin as the matrix resin was 1050 MPa.

Examples 22 to 24

Carbon fibers were obtained as described for Example 14, except thatpentaerythritol triacrylate hexamethylene diisocyanate (monomer B),phenyl glycidyl ether acrylate hexamethylene diisocyanate (monomer C) orpentaerythritol triacrylate tolylene diisocyanate (monomer E: molecularweight 770) was used as the monomer. Respective properties of thecomposite materials with the vinyl ester resin as the matrix resin weremeasured and the results are shown in Table 5.

Examples 25 and 26

Carbon fibers were obtained as described for Example 14, except thatpolyoxyethylene styrenated phenyl ether (emulsifying agent B) orpolyoxyethylene (40-mole) styrenated (5-mole) cumylphenol (emulsifyingagent C) was used as the emulsifying agent. Respective properties of thecomposite materials with the vinyl ester resin as the matrix resin weremeasured and the results are shown in Table 5.

Example 27

The ILSS of the composite material consisting of the polymer depositedcarbon fibers obtained in Example 14 and the unsaturated polyester resinwas 83 MPa, and the ILSS of the composite material after waterabsorption was 66 MPa.

Comparative Example 5

The ILSS of the composite material consisting of the polymer depositedcarbon fibers obtained in Comparative Example 3 and the unsaturatedpolyester resin was 52 MPa, and the ILSS of the composite material afterwater absorption was 48 MPa.

Example 28

To obtain a polymer having urethane groups as the polar groups and vinylgroups as the groups capable of reacting with the phenol resin, amixture consisting of glycerol dimethacrylate hexamethylene diisocyanate(monomer A) and 2-allylphenol (ratio by weight 50:50) was used as themonomer, and its acetone solution was prepared as the sizing solution.It was applied to the raw carbon fibers used in Example 1 by immersion,and the carbon fibers impregnated with the sizing solution were dried bya 150° C. hot drying roller for 5 seconds and in succession treated by ahot air circulation type dryer at 230° C. for 60 seconds for thermalpolymerization. The deposited amount of all the deposit was 0.5 wt %,and the deposited amount of the polymer component insoluble in methanolwas 0.05 wt %.

The ILSS and the bending strength of the composite material consistingof the obtained carbon fibers and the phenol resin are shown in Table 6.The ILSS was 59 MPa, and the bending strength was 1780 MPa, showing highadhesion properties. The abrasion fluff was 4 pieces/m, and theflexibility of the carbon fiber bundle was good, showing highsophisticated processability.

Examples 29 to 33

Carbon fibers were obtained as described for Example 28, except that amixture consisting of glycerol dimethacrylate hexamethylene diisocyanateand phenoxyethyl acrylate, a mixture consisting of glyceroldimethacrylate hexamethylene diisocyanate and phenoxy polyethyleneglycol methacrylate, a mixture consisting of glycerol dimethacrylatehexamethylene diisocyanate and 2-hydroxy-3-phenoxypropyl methacrylate,phenylglycidyl ether acrylate hexamethylene diisocyanate (monomer C) orphenylglycidyl ether acrylate tolylene diisocyanate (monomer D) was usedas the monomer.

The ILSSs and bending strengths of the composite materials consisting ofthe obtained carbon fibers and the phenol resin are shown in Table 6.

Example 34

Carbon fibers were obtained as described for Example 28, except thatphenylglycidyl ether acrylate tolylene diisocyanate (monomer D) was usedas the monomer and that the nonionic emulsifying agent was added to thesizing solution, to make an emulsion (the ratio by weight of the monomerD: the nonionic emulsifying agent was 80:20). The abrasion fluff was 5pieces/m and the flexibility of the CF bundle was good. The ILSS of thecomposite material consisting of the obtained carbon fibers and thephenol resin is shown in Table 6.

Comparative Examples 6 and 7

Carbon fibers were obtained as described for Example 28, except thatbisphenol A diglycidyl ether alone or glycerol dimethacrylatehexamethylene diisocyanate alone was used as the monomer. The ILSSs andthe bending strengths of the composite materials consisting of theobtained carbon fibers and the phenol resin are shown in Table 6.

Example 35

Raw carbon fibers were obtained as described for Example 1, except thatthe electrolytic surface treatment was effected using an aqueoussolution of ammonium hydrogencarbonate with a concentration of 3mole/liter as the electrolyte at 80 coulombs/g-CF. The surface oxygenconcentration ratio O/C of the raw carbon fibers was 0.14, and thesurface carboxyl group concentration COOH/C ratio was 1.3%. Insuccession, to obtain a polymer having hydantoin structures as the polargroups and epoxy groups as the groups capable of reacting with the epoxyresin, the reaction product between dimethylhydantoin and hexamethylenediglycidyl ether was used as the monomer, and its ethanol solution wasprepared. It was applied to the raw carbon fibers by immersion. Thecarbon fibers impregnated with the ethanol solution was dried by a 150°C. hot drying roller for 5 seconds and in succession treated by a hotair circulation type dryer at 210° C. for 60 seconds for thermalpolymerization. The deposited amount of all the deposit was 0.5 wt %,and the deposited amount of the polymer component insoluble inchloroform was 0.05 wt %.

The ILSS of the composite material consisting of the obtained carbonfibers and the epoxy resin is shown in Table 7. The ILSS was 90 MPa,showing high adhesion properties. The abrasion fluff was 3 pieces/m, andthe flexibility of the CF bundle was good, showing high sophisticatedprocessability. The compressive strength of the composite material was1560 MPa.

Examples 36 to 39

Carbon fibers were obtained as described for Example 33, except that areaction product between dimethylhydantoin and diethylene glycoldiglycidyl ether, a reaction product between dimethylhydantoin andpolymethylolpropane polyglycidyl ether, a reaction product betweentrihexamethylene isocyanurate and glycidol or a mixture consisting ofglycerol dimethacrylate hexamethylene diisocyanate (monomer A) andglycidyl methacrylate ethylene oxide (5-mole) propylene oxide (2-mole)addition product (ratio by weight 50:50) was used as the monomer. TheILSSs of the composite materials consisting of the obtained carbonfibers and the epoxy resin are shown in Table 7.

Comparative Examples 8 and 9

Carbon fibers were obtained as described for Example 34, except thatbisphenol A diglycidyl ether alone or glycerol dimethacrylatehexamethylene diisocyanate alone was used as the monomer. The ILSSs ofthe composite materials consisting of the obtained carbon fibers and theepoxy resin are shown in Table 7. The compressive strength ofComparative Example 8 was 1460 GPa.

TABLE 1 (Vinyl ester resin) Polar group density Number of Polymerization(×10⁻³ piece/ unsaturated groups temperature ILSS O/C COOH/C Monomermolecular weight) at ends (pieces) (° C.) (MPa) Example 1 0.10 1.2%Glycerol dimethacrylate 3.2 4 230 85 hexamethylene diisocyanate Example2 0.10 1.2% Pentaerythritol triacrylate 2.6 6 230 86 hexamethylenediisocyanate Example 3 0.10 1.2% Phenylglycidyl ether 3.4 2 230 81acrylate hexamethylene diisocyanate Example 4 0.10 1.2% Phenylglycidylether 3.4 2 230 79 acrylate tolylene diisocyanate Comparative 0.10 1.2%Trimethylolpropane 0 3 230 75 Example 1 triacrylate Comparative 0.101.2% — — — 230 76 Example 2 Comparative 0.10 1.2% Bisphenol A diglycidyl0 0 230 77 Example 3 ether Example 5 0.15 2.1% Glycerel dimethacrylate3.2 4 230 86 hexamethylene diisocyanate Example 6 0.20 2.4% Glyceroldimethacrylate 3.2 4 230 84 hexamethylene diisocyanate Example 7 0.090.5% Glycerol dimethacrylate 3.2 4 230 80 hexamethylene diisocyanate

TABLE 2 (Vinyl ester resin) Polar group density Number of Polymerization(×10⁻³ piece/ unsaturated groups temperature ILSS ILSS after waterRetension Monomer molecular weight) at ends (pieces) (° C.) (MPa)absorption (MPa) ratio (%) Example 1 Glycerol dimethacrylate hexa- 3.2 4230 85 77 91 methylene diisocyanate Example 8 Glycerol dimethacrylatehexa- 3.2 4 180 84 76 90 methylene diisocyanate Example 9 Glyceroldimethacrylate hexa- 3.2 4 150 81 69 85 methylene diisocyanate Example10 Glycerol dimethacrylate hexa- 3.2 4 80 80 60 75 methylenediisocyanate

TABLE 3 (Vinyl ester resin) Polar group density Number of Polymerization(×10⁻³ piece/ unsaturated groups temperature ILSS O/C COOH/C Monomermolecular weight) at ends (pieces) (° C.) (MPa) Example 1 0.10 1.2%Glycerol dimethacrylate 3.2 4 230 85 hexamethylene diisocyanate Example11 0.10 1.2% Bisphenol S diglycidyl 3.2 2 230 80 methacrylate Example 120.10 1.2% N,N-dimethylaminoethyl 7.0 1 230 79 acrylate Example 13 0.101.2% End acryl modified liquid 2.0 >5 230 78 butadiene

TABLE 4 (Vinyl ester resin) Deposited Deposited amount amount of matterILSS of all insoluble Abrasion Flexibility after water Retention BendingEmulsifying Ingredient the deposit in styrene fluff of ILSS absorptionratio strength Monomer Solvent agent ratio (wt %) (wt %) (pieces/m) CFbundle (MPa) (Mpa) (%) (MPa) Example A Water A 90:10 0.5 0.15 3 Good 8477 92 1350 14 Example A Water A 80:20 0.5 0.13 3 Good 83 74 89 1330 15Example A Water A 70:30 0.5 0.15 3 Good 79 65 82 1280 16 Example A WaterA 60:40 0.5 0.05 2 Good 75 60 80 1250 17 Example A Water A 90:10 0.50.05 4 Good 81 70 86 1290 18 Example A Water A 90:10 0.5 0.10 3 Good 8376 92 1310 19 Example A Water A 90:10 1.0 0.30 2 Rather 85 79 93 1340 20poor Example A Water A 90:10 0.1 0.02 15  Rather 78 63 84 1270 21 poorCompara- Ep828 Water A 90:10 0.5 0.11 6 Rather 76 56 74 1240 tive Ex-poor ample 4

TABLE 5 (Vinyl ester resin) Deposited Deposited amount amount of matterILSS of all insoluble Abrasion Flexibility after water Retention BendingEmulsifying Ingredient the deposit in styrene fluff of ILSS absorptionratio strength Monomer Solvent agent ratio (wt %) (wt %) (pieces/m) CFbundle (MPa) (Mpa) (%) (MPa) Example A Water A 90:10 0.5 0.15 3 good 8477 92 1350 14 Example C Water A 90:10 0.5 0.12 3 good 85 77 91 1370 22Example B Water A 90:10 0.5 0.18 3 good 83 76 92 1340 23 Example E WaterA 90:10 0.5 0.15 4 good 82 75 92 1320 24 Example A Water B 90:10 0.50.16 3 good 84 77 92 1340 25 Example A Water C 90:10 1.5 0.15 2 good 8376 92 1320 26

TABLE 6 (Phenol resin) Bending ILSS strength Monomer (MPa) (MPa) Example28 Glycerol dimethacrylate hexamethylene 59 1780 diisocyanate and2-allylphenol Example 29 Glycerol dimethacrylate hexamethylene 53 —diisocyanate and phenoxyethyl mono- acrylate Example 30 Glyceroldimethacrylate hexamethylene 53 — diisocyanate and phenoxy diethyleneglycol monomethacrylate Example 31 Glycerol dimethacrylate hexamethylene54 — diisocyanate and hydroxy-3-phenoxy- propyl monomethacrylate Example32 Phenylglycidyl ether acrylate hexa- 61 — methylene diisocyanateExample 33 Phenylglycidyl ether acrylate tolylene 62 1820 diisocyanateExample 34 Phenylglycidyl ether acrylate tolylene 60 — diisocyanate(nonionic emulsifying agent) Comparative Bisphenol A glycidyl ether 431660 Example 6 Comparative Glycerol dimethacrylate hexamethylene 49 —Example 7 diisocyanate

TABLE 7 (Epoxy resin) ILSS Monomer (MPa) Example 35 Reaction productbetween dimethylhydantoin and 90 hexamethylene diglycidyl ether Example36 Reaction product between dimethylhydantoin and 90 diethylene glycoldiglycidyl ether Example 37 Reaction product between dimethylhydantoinand 90 polymethylolpropane polyglycidyl ether Example 38 Reactionproduct between trihexamethylene 90 isocyanurate and glycidol Example 39Glycerol dimethacrylate hexamethylene 88 diisocyanate and glycidylmethacrylate ethylene oxide (5-mole) propylene oxide (2-mole) additionproduct Comparative Bisphenol A diglycidyl ether 83 Example 8Comparative Glycerol dimethacrylate hexamethylene 83 Example 9diisocyanate

INDUSTRIAL APPLICABILITY

The present invention can provide carbon fibers unlikely to causefluffing and fiber breaking even when rubbed by guide bars and rollersin sophisticated processing, excellent in adhesion properties to thematrix resin, and also excellent in the bending properties andcompressive properties of the composite material obtained using thecarbon fibers.

The carbon fibers of the present invention in combination with anunsaturated polyester resin or vinyl ester resin can be preferably usedfor small ships, boats, yachts, fishing boats, household waste watertreatment tanks, various other tanks, etc., and the carbon fibers of thepresent invention in combination with a phenol resin can be preferablyused for interior materials of transport vehicles such as airplanes,architectural members such as trusses, etc.

What is claimed is:
 1. Carbon fibers having a composition deposited onthe fiber surface comprising a polymer having at least one polar groupand at least one group capable of reacting with a matrix resin, whereinthe polymer is substantially insoluble in a matrix resin and the polargroup is selected from amido groups, imido groups, urethane groups, ureagroups, isocyanate groups, sulfo groups, and mixtures thereof, thematrix resin is selected from an unsaturated polyester resin, vinylester resin and phenol resin, groups capable of reacting with the matrixresin selected from hydroxyphenoxy groups, phenoxy groups, phenolichydroxyl groups, vinyl groups, acrylate groups, methacrylate groups andmixtures thereof, and the fiber surfaces have a surface oxygenconcentration O/C ratio of from about 0.02 to about 0.3 as measured byX-ray photoelectron spectroscopy, wherein the monomer comprising thepolymer comprises a reaction product of 1) an unsaturated alcohol ; 2)an isocyanate compound, 3) an aromatic compound having unsaturatedgroups at the ends, and 4) at least one group selected fromhydroxybenzyl groups, hydroxyphenoxy groups, phenoxy groups and phenolichydroxyl groups.